FIELD OF THE INVENTION

The invention relates to a method for automatically adjusting a multiple-input-port and multiple-output-port tuning unit of a radio transceiver using several antennas simultaneously to communicate in a wireless network, the wireless network being possibly a cellular wireless network. The invention also relates to a radio transceiver using this method.

The French patent application No. FR1870421 of 9 April 2018, entitled“Precede pour reglage automatique d’une unite d’accord, et emetteur-recepteur radio utilisant ce precede” is incorporated by reference.

PRIOR ART

In what follows, in line with the“IEC multilingual dictionary of electricity” edited by the Bureau Central de la Commission Electrotechnique Internationale in 1983 ,“open-loop control” means control which does not utilize a measurement of the controlled variable, and“closed-loop control” (which is also referred to as“feedback control”) means control in which the control action is made to depend on a measurement of the controlled variable.

Tuning an impedance matrix means obtaining that an impedance matrix presented by a plurality of input ports of a device approximates a wanted impedance matrix, and simultaneously offering an ideally lossless, or nearly lossless, transfer of power from the plurality of input ports to a plurality of output ports of the device, in a context where the impedance matrix seen by the plurality of output ports may vary. Thus, if the ports of a multiport signal generator presenting an impedance matrix equal to the hermitian adjoint (that is to say a matrix equal to the matrix transpose of the matrix complex conjugate) of the wanted impedance matrix are suitably connected to the plurality of input ports, said multiport signal generator delivers a maximum power to the plurality of input ports, and the plurality of output ports delivers a power near this maximum power.

A multiple-input-port and multiple-output-port tuning unit behaves, at any frequency in a given frequency band, with respect to its input ports and output ports, substantially as a passive linear device, where“passive” is used in the meaning of circuit theory. More precisely, a multiple-input-port and multiple-output-port tuning unit behaves, at any frequency in a given frequency band, with respect to its n output ports and m input ports, where n and m are nonzero integers, substantially as a passive linear ( n + m)-port device. As a consequence of linearity, it is possible to define the impedance matrix presented by the input ports. As a consequence of passivity, the multiple-input-port and multiple-output-port tuning unit does not provide amplification. A multiple-input-port and multiple-output-port tuning unit comprises several adjustable impedance devices each having an adjustable reactance. Adjusting a multiple-input- port and multiple-output-port tuning unit means adjusting the reactance of one or more of its adjustable impedance devices. A multiple-input-port and multiple-output-port tuning unit may be used for tuning an impedance matrix. To tune an impedance matrix, the multiple-input-port and multiple-output-port tuning unit must be properly adjusted, that is to say, the reactances of its adjustable impedance devices must be properly adjusted.

An adjustable impedance device is a component comprising two terminals which substantially behave as the terminals of a passive linear two-terminal circuit element, and which are consequently characterized by an impedance which may depend on frequency, this impedance being adjustable.

An adjustable impedance device having a reactance which is adjustable by electrical means may be such that it only provides, at a given frequency, a finite set of reactance values, this characteristic being for instance obtained if the adjustable impedance device is:

- a network comprising a plurality of capacitors or open-circuited stubs and one or more electrically controlled switches or change-over switches, such as electro-mechanical relays, or microelectromechanical switches, or PIN diodes or insulated-gate field-effect transistors, used to cause different capacitors or open-circuited stubs of the network to contribute to the reactance; or

- a network comprising a plurality of coils or short-circuited stubs and one or more electrically controlled switches or change-over switches used to cause different coils or short-circuited stubs of the network to contribute to the reactance.

An adjustable impedance device having a reactance which is adjustable by electrical means may be such that it provides, at a given frequency, a continuous set of reactance values, this characteristic being for instance obtained if the adjustable impedance device is based on the use of a variable capacitance diode; or a MOS varactor; or a microelectromechanical varactor (MEMS varactor); or a ferroelectric varactor.

The patent of the United States of America No. 9,077,317, entitled“Method and apparatus for automatically tuning an impedance matrix, and radio transmitter using this apparatus”, discloses a first method for automatically tuning an impedance matrix, this method using m or more different excitations applied successively to the input ports. Unfortunately, this method is usually not compatible with the specifications of a radio transmitter used for MIMO wireless communication, because the generation of a sequence of m or more different excitations applied successively entails a prolonged emission of electromagnetic waves, which is usually not compatible with the requirements of all MIMO emission modes of applicable standards, for instance the LTE-Advanced standards.

This problem is solved in a second method for automatically tuning an impedance matrix, disclosed in the international application number PCT/IB2015/057131 of 16 September 2015 (WO 2016/207705), in which the excitations need not be applied successively. A block diagram of a system implementing the first method for automatically tuning an impedance matrix, or the second method for automatically tuning an impedance matrix, is shown in Figure 1. This system is a part of an apparatus for radio communication. The system shown in Fig. 1 has m = 4 user ports (311) (321) (331) (341), the m user ports presenting, at a given frequency, an impedance matrix referred to as“the impedance matrix presented by the user ports”, the system comprising:

n = 4 antennas (11) (12) (13) (14), the n antennas operating simultaneously in a given frequency band, the n antennas forming a multiport antenna array (1);

m sensing units (31) (32) (33) (34), each of the sensing units delivering two“sensing unit output signals”, each of the sensing unit output signals being determined by one electrical variable sensed (or measured) at one of the user ports;

a multiple-input-port and multiple-output-port tuning unit (4) having m input ports and n output ports, each of the input ports being coupled to one and only one of the user ports through one and only one of the sensing units, the multiple-input-port and multiple-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to m, the p adjustable impedance devices being referred to as the“adjustable impedance devices of the tuning unit” and being such that, at said given frequency, each of the adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the adjustable impedance devices of the tuning unit being adjustable by electrical means;

n feeders (21) (22) (23) (24), each of the feeders having a first end coupled to a signal port of one and only one of the antennas, each of the feeders having a second end coupled to one and only one of the output ports;

a signal processing unit (5), the signal processing unit estimating q real quantities depending on the impedance matrix presented by the user ports, where q is an integer greater than or equal to m, using the sensing unit output signals caused by m excitations applied to the user ports, the signal processing unit delivering an“adjustment instruction” as a function of said q real quantities depending on the impedance matrix presented by the user ports; and

a control unit (6), the control unit receiving the adjustment instruction from the signal processing unit (5), the control unit delivering“control signals”, the control signals being determined as a function of the adjustment instruction, the reactance of each of the adjustable impedance devices of the tuning unit being mainly determined by at least one of the control signals.

The first method for automatically tuning an impedance matrix and the second method for automatically tuning an impedance matrix are based on closed-loop control, and they do not include the description of a fast control technique, so that a full automatic adjustment of the multiple-input-port and multiple-output-port tuning unit requires several iterations, each iteration comprising the following steps: applying m excitations to the m user ports; estimating q real quantities depending on the impedance matrix presented by the user ports; delivering an adjustment instruction; and delivering control signals. In order to be compatible with the requirements of the standards typically applicable to MIMO wireless networks, each iteration must typically use, for the excitations, one or more data symbols (for instance OFDMA or SC- FDMA data symbols) comprising resource elements allocated to reference signals (also referred to as“pilots”) for MIMO channel estimation. This has two undesirable consequences: first, the reference signals of a data symbol used for the excitations of an iteration give an incorrect estimate of the MIMO channel, since the channel is modified at the end of the iteration; and second, said full automatic adjustment is very slow, because the reference signals are not very frequent.

A third method for automatically tuning an impedance matrix is disclosed in the international application number PCT/IB2015/057161 of 17 September 2015 (WO 2017/033048). A block diagram of a system implementing the third method for automatically tuning an impedance matrix is shown in Figure 2. This system is a part of an apparatus for radio communication. The system shown in Fig. 2 has m = 4 user ports (311) (321) (331) (341), the system comprising:

n = 4 antennas (11) (12) (13) (14), the n antennas operating simultaneously in a given frequency band, the n antennas forming a multiport antenna array (1);

a multiple-input-port and multiple-output-port tuning unit (4) having m input ports and n output ports, each of the input ports being coupled to one and only one of the user ports, the multiple-input-port and multiple-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to m, the p adjustable impedance devices being referred to as the“adjustable impedance devices of the tuning unit” and being such that, at said given frequency, each of the adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the adjustable impedance devices of the tuning unit being adjustable by electrical means; n sensing units (31) (32) (33) (34), each of the sensing units delivering two“sensing unit output signals”, each of the sensing unit output signals being determined by one electrical variable sensed (or measured) at one of the output ports;

n feeders (21) (22) (23) (24), each of the feeders having a first end which is directly coupled to a signal port of one and only one of the antennas, each of the feeders having a second end which is indirectly coupled to one and only one of the output ports, through one and only one of the sensing units;

a signal processing unit (5), the signal processing unit estimating q real quantities depending on an impedance matrix seen by the output ports, where q is an integer greater than or equal to m, using the sensing unit output signals caused by m excitations applied to the user ports, the signal processing unit delivering an“adjustment instruction” as a function of said q real quantities depending on an impedance matrix seen by the output ports; and

a control unit (6), the control unit receiving the adjustment instruction from the signal processing unit (5), the control unit delivering“control signals”, the control signals being determined as a function of the adjustment instruction, the reactance of each of the adjustable impedance devices of the tuning unit being mainly determined by at least one of the control signals.

The third method for automatically tuning an impedance matrix is based on open-loop control, so that it may be fast, if properly implemented. In order to be compatible with the requirements of the standards typically applicable to MIMO wireless networks, the third method must typically use, for the excitations, one or more data symbols comprising resource elements allocated to reference signals for MIMO channel estimation. This has an undesirable consequence: the reference signals of a data symbol used for the excitations give an incorrect estimate of the MIMO channel, since the channel is modified when the control signals are delivered.

Thus, the prior art does not teach a method for automatically tuning an impedance matrix, which is sufficiently fast, which is compatible with the requirements of the standards typically applicable to MIMO wireless networks, and which does not entail an incorrect estimate of the MIMO channel.

SUMMARY OF THE INVENTION

The purpose of the invention is a method for automatically adjusting a multiple-input-port and multiple-output-port tuning unit, without the above-mentioned limitations of known techniques, and also a radio transceiver using this method.

In what follows, X and Y being different quantities or variables, performing an action as a function of X does not preclude the possibility of performing this action as a function of Y. In what follows,“having an influence” and“having an effect” have the same meaning. In what follows,“coupled”, when applied to two ports (in the meaning of circuit theory), may indicate that the ports are directly coupled, in which case each terminal of one of the ports is connected to (or, equivalently, in electrical contact with) one and only one of the terminals of the other port, and/or that the ports are indirectly coupled, in which case an electrical interaction different from direct coupling exists between the ports, for instance through one or more components.

The method of the invention is a method for automatically adjusting a multiple-input-port and multiple-output-port tuning unit, the multiple-input-port and multiple-output-port tuning unit having m input ports and n output ports, where m and n are each an integer greater than or equal to 2, the multiple-input-port and multiple-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to m, the p adjustable impedance devices being referred to as the“adjustable impedance devices of the tuning unit” and being such that, at a given frequency, each of the adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the adjustable impedance devices of the tuning unit being adjustable by electrical means, the reactance of any one of the adjustable impedance devices of the tuning unit being mainly determined by at least one tuning control signal, the multiple-input-port and multiple-output-port tuning unit being a part of a radio transceiver comprising N antennas used to communicate in a wireless network, where N is an integer greater than or equal to 2, the radio transceiver allowing, at the given frequency, a transfer of power from the m input ports to an electromagnetic field radiated by the antennas, the method comprising the steps of:

receiving, from the wireless network, a radio signal providing an authorization to use, for excitations intended for an adjustment, one or more data symbols, each of said data symbols being referred to as“authorized data symbol”;

applying m excitations to the in input ports, one and only one of the excitations being applied to each of the input ports, the excitations existing inside one or more of the one or more authorized data symbols;

sensing one or more electrical variables at each of the input ports, to obtain“sensing unit output signals”, each of the sensing unit output signals being mainly determined by at least one of the electrical variables sensed at one of the input ports;

estimating q real quantities depending on an impedance matrix presented by the input ports, where q is an integer greater than or equal to m, by utilizing the sensing unit output signals; and

utilizing said q real quantities depending on an impedance matrix presented by the input ports, to obtain the one or more tuning control signals.

The method of the invention may for instance be such that the radio transceiver requests, from the wireless network, a permission to use, for excitations intended for an adjustment, one or more data symbols; and that, afterwards, the radio transceiver receives said radio signal providing an authorization. In this case, the method of the invention may for instance be such that the radio transceiver specifies the one or more data symbols to which said authorization applies.

The method of the invention may for instance be such that the wireless network specifies the one or more data symbols to which said authorization applies.

The method of the invention may for instance be such that the excitations exist only inside one or more resource elements of the one or more authorized data symbols.

The given frequency may for instance be a frequency greater than or equal to 150 MHz. The specialist understands that an impedance matrix seen by the output ports is a complex matrix of size n by n, and that an impedance matrix presented by the input ports is a complex matrix of size m by m. We will use Z _Sant to denote the impedance matrix seen by the output ports, and Z, _: to denote the impedance matrix presented by the input ports. Each of these matrices depends on the frequency. Z, · also depends on the one or more tuning control signals, so that the method of the invention uses closed-loop control.

Each of the N antennas has a port, referred to as the“signal port” of the antenna, which can be used to receive and/or to emit electromagnetic waves. It is assumed that each of the antennas behaves, at the given frequency, with respect to the signal port of the antenna, substantially as a passive antenna, that is to say as an antenna which is linear and does not use an amplifier for amplifying signals received by the antenna or signals emitted by the antenna. As a consequence of linearity, it is possible to define an impedance matrix presented by the antennas, the definition of which only considers, for each of the antennas, the signal port of the antenna. This matrix is consequently of size N x N. Because of the interactions between the antennas, this matrix need not be diagonal. In particular, the invention may for instance be such that this matrix is not a diagonal matrix.

It is said above that the radio transceiver allows, at the given frequency, a transfer of power from the m input ports to an electromagnetic field radiated by the antennas. In other words, the radio transceiver is such that, if a power is received by the m input ports at the given frequency, a part of said power received by the m input ports is transferred to an electromagnetic field radiated by the antennas at the given frequency, so that a power of the electromagnetic field radiated by the antennas at the given frequency is equal to said part of said power received by the m input ports. For instance, the specialist knows that a power of the electromagnetic field radiated by the antennas (average radiated power) can be computed as the flux of the real part of a complex Poynting vector of the electromagnetic field radiated by the antennas, through a closed surface containing the antennas.

To obtain that the radio transceiver allows, at the given frequency, a transfer of power from the m input ports to an electromagnetic field radiated by the antennas, each of the antennas may, if n = N, for instance be coupled, directly or indirectly, to one and only one of the output ports, as shown below in the presentation of the first embodiment. More precisely, if n = N, for each of the antennas, the signal port of the antenna may for instance be coupled, directly or indirectly, to one and only one of the output ports. For instance, an indirect coupling may be a coupling through a feeder. For suitable values of the one or more tuning control signals, said transfer of power from the m input ports to an electromagnetic field radiated by the antennas may for instance be a transfer of power with small or negligible or zero losses, this characteristic being preferred.

The method of the invention may for instance be such that any diagonal entry of the impedance matrix presented by the input ports is influenced by the reactance of at least one of the adjustable impedance devices of the tuning unit. The method of the invention may for instance be such that the reactance of at least one of the adjustable impedance devices of the tuning unit has an influence on at least one non-diagonal entry of the impedance matrix presented by the input ports. An apparatus implementing the method of the invention is a radio transceiver for communicating in a wireless network, the radio transceiver comprising:

N antennas, where N is an integer greater than or equal to 2;

a multiple-input-port and multiple-output-port tuning unit having m input ports and n output ports, where m and n are each an integer greater than or equal to 2, the radio transceiver allowing, at a given frequency, a transfer of power from the m input ports to an electromagnetic field radiated by the antennas, the multiple-input-port and multiple-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to m, the p adjustable impedance devices being referred to as the“adjustable impedance devices of the tuning unit” and being such that, at the given frequency, each of the adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the adjustable impedance devices of the tuning unit being adjustable by electrical means;

m sensing units, each of the sensing units delivering one or more“sensing unit output signals”, each of the sensing unit output signals being mainly determined by one or more electrical variables sensed at one of the input ports;

a radio unit, the radio unit receiving, from the wireless network, a radio signal providing an authorization to use, for excitations intended for an adjustment, one or more data symbols, each of said data symbols being referred to as“authorized data symbol”, the radio unit being utilized to apply m excitations to the m input ports, one and only one of the excitations being applied to each of the input ports, the excitations existing inside one or more of the one or more authorized data symbols, the radio unit estimating q real quantities depending on an impedance matrix presented by the input ports, where q is an integer greater than or equal to m, by utilizing the sensing unit output signals, the radio unit delivering one or more“tuning unit adjustment instructions”, at least one of the one or more tuning unit adjustment instructions being determined as a function of the q real quantities depending on an impedance matrix presented by the input ports; and

a control unit, the control unit delivering one or more“tuning control signals”, each of the one or more tuning control signals being determined as a function of at least one of the one or more tuning unit adjustment instructions, the reactance of each of the adjustable impedance devices of the tuning unit being mainly determined by at least one of the one or more tuning control signals.

For instance, each of said electrical variables may be a voltage, or an incident voltage, or a reflected voltage, or a current, or an incident current, or a reflected current.

As explained above, if n = N, it is for instance possible that each of the antennas is coupled, directly or indirectly, to one and only one of the output ports. As explained above, if n = N, it is for instance possible that, for each of the antennas, the signal port of the antenna is coupled, directly or indirectly, to one and only one of the output ports. Thus, said transfer of power (from the m input ports to an electromagnetic field radiated by the antennas) may take place through the multiple-input-port and multiple-output-port tuning unit. The integer p may be greater than or equal to 2m.

It is for instance possible that each of the m input ports is coupled, directly or indirectly, to a port of the radio unit, said port of the radio unit delivering one and only one of the excitations.

For instance, it is possible that the reactance of any one of the adjustable impedance devices of the tuning unit has an influence on an impedance matrix presented by the input ports.

The specialist understands that the radio transceiver of the invention is adaptive in the sense that the reactances of the adjustable impedance devices of the tuning unit are varied with time as a function of the sensing unit output signals, which are each mainly determined by one or more electrical variables.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics will appear more clearly from the following description of particular embodiments of the invention, given by way of non-limiting examples, with reference to the accompanying drawings in which:

Figure 1 shows a block diagram of an automatic adjustment system, and has already been discussed in the section dedicated to the presentation of the prior art;

Figure 2 shows a block diagram of an automatic adjustment system, and has already been discussed in the section dedicated to the presentation of the prior art;

Figure 3 shows a block diagram of a radio transceiver of the invention;

Figure 4 shows a resource grid of a wireless network.

DETAILED DESCRIPTION OF SOME EMBODIMENTS First embodiment. As a first embodiment of a device of the invention, given by way of non-limiting example, we have represented in Figure 3 the block diagram of a radio transceiver for communicating in a wireless network, the radio transceiver comprising:

N = 4 antennas (11) (12) (13) (14), the antennas operating simultaneously in a given frequency band, the antennas forming a multiport antenna array (1);

a multiple-input-port and multiple-output-port tuning unit (4) having m = 4 input ports and n = N output ports, the multiple-input-port and multiple-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to 2m = 8, the p adjustable impedance devices being referred to as the“adjustable impedance devices of the tuning unit” and being such that, at a given frequency greater than or equal to 300 MHz, each of the adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the adjustable impedance devices of the tuning unit being adjustable by electrical means;

m sensing units (31) (32) (33) (34), each of the sensing units delivering two“sensing unit output signals”, each of the sensing unit output signals being determined by an electrical variable sensed (or measured) at one of the input ports;

N feeders (21) (22) (23) (24), each of the feeders having a first end which is directly coupled to a signal port of one and only one of the antennas, each of the feeders having a second end which is directly coupled to one and only one of the output ports; a radio unit (8), the radio unit receiving, from the wireless network, a radio signal providing an authorization to use, for excitations intended for an internal adjustment of the radio transceiver, one or more data symbols, each of said data symbols being referred to as “authorized data symbol”, the radio unit applying m excitations to the m input ports through the sensing units, one and only one of the excitations being applied to each of the input ports, the excitations existing inside one or more of the one or more authorized data symbols, the radio unit estimating q real quantities depending on an impedance matrix presented by the input ports, where q is an integer greater than or equal to m, by utilizing the sensing unit output signals, the radio unit delivering one or more“tuning unit adjustment instructions”, at least one of the one or more tuning unit adjustment instructions being determined as a function of the q real quantities depending on an impedance matrix presented by the input ports; and

a control unit (6), the control unit receiving the one or more tuning unit adjustment instructions, the control unit delivering one or more“tuning control signals” to the multiple-input-port and multiple-output-port tuning unit, each of the one or more tuning control signals being determined as a function of at least one of the one or more tuning unit adjustment instructions, the reactance of each of the adjustable impedance devices of the tuning unit being mainly determined by at least one of the one or more tuning control signals.

Each of the antennas is coupled to one and only one of the output ports. More precisely, for each of the antennas, the signal port of the antenna is indirectly coupled to one and only one of the output ports, through one and only one of the feeders. Moreover, each of the output ports is coupled to one and only one of the antennas. More precisely, each of the output ports is indirectly coupled to the signal port of one and only one of the antennas, through one and only one of the feeders. The given frequency lies in the given frequency band. The given frequency band only contains frequencies greater than or equal to 300 MHz.

Each of the sensing units (31) (32) (33) (34) may for instance be such that the two sensing unit output signals delivered by said each of the sensing units comprise: a first sensing unit output signal proportional to a first electrical variable, the first electrical variable being a voltage across one of the input ports; and a second sensing unit output signal proportional to a second electrical variable, the second electrical variable being a current flowing in said one of the input ports. Said voltage across one of the input ports may be a complex voltage and said current flowing in said one of the input ports may be a complex current. Alternatively, each of the sensing units (31) (32) (33) (34) may for instance be such that the two sensing unit output signals delivered by said each of the sensing units comprise: a first sensing unit output signal proportional to a first electrical variable, the first electrical variable being an incident voltage (which may also be referred to as“forward voltage”) at one of the input ports; and a second sensing unit output signal proportional to a second electrical variable, the second electrical variable being a reflected voltage at said one of the input ports. Said incident voltage at one of the input ports may be a complex incident voltage and said reflected voltage at said one of the input ports may be a complex reflected voltage.

Each of the m input ports is indirectly coupled to a port of the radio unit (8), through one and only one of the sensing units, said port of the radio unit delivering one and only one of the excitations. Each of the one or more tuning unit adjustment instructions may be of any type of digital message. The one or more tuning unit adjustment instructions are delivered during one or more adjustment sequences. The duration of an adjustment sequence is less than 100 microseconds. The specialist understands that the radio transceiver uses closed-loop control to automatically adjust the multiple-input-port and multiple-output-port tuning unit.

The multiple-input-port and multiple-output-port tuning unit (4) is such that, at said given frequency, if the impedance matrix seen by the output ports is equal to a given non-diagonal impedance matrix, a mapping associating the impedance matrix presented by the input ports to the p reactances is defined, the mapping having, at a given value of each of the p reactances, a partial derivative with respect to each of the p reactances, a span of the p partial derivatives being defined in the set of the complex matrices of size m by m considered as a real vector space, any diagonal complex matrix of size m by m having the same diagonal entries as at least one element of the span of the p partial derivatives. This must be interpreted as meaning: the multiple-input-port and multiple-output-port tuning unit is such that, at said given frequency, there exists a non-diagonal impedance matrix referred to as the given non-diagonal impedance matrix, the given non-diagonal impedance matrix being such that, if an impedance matrix seen by the output ports is equal to the given non-diagonal impedance matrix, then a mapping associating an impedance matrix presented by the input ports to the p reactances is defined, the mapping having, at a given value of each of the p reactances, a partial derivative with respect to each of the p reactances, a span of the p partial derivatives being defined in the set of the complex matrices of size m by m considered as a real vector space, any diagonal complex matrix of size m by m having the same diagonal entries as at least one element of the span of the p partial derivatives. The specialist knows that the dimension of the span of the p partial derivatives considered as a real vector space has been used and explained: in the international application number PCT/IB2013/058423 (WO 2014/049475); and in the sections I, III, VI, VII and VIII of the article of F. Broyde and E. Clavelier entitled“Some Properties of Multiple-Antenna-Port and Multiple-User-Port Antenna Tuners”, published in IEEE Trans on Circuits and Systems— I: Regular Papers, Vol. 62, No. 2, pp. 423-432, in February 2015. In said article, said dimension of the span of the p partial derivatives is referred to as the local dimension of the user port impedance range, and denoted by D _UR (Z„„). A specialist understands that, to obtain that any diagonal complex matrix of size m by m has the same diagonal entries as at least one element of the span of the p partial derivatives, it is necessary that the dimension of the span of the p partial derivatives considered as a real vector space is greater than or equal to the dimension of the subspace of the diagonal complex matrices of size m by m considered as a real vector space. Since the dimension of the span of the p partial derivatives considered as a real vector space is less than or equal to p, and since the dimension of the subspace of the diagonal complex matrices of size m by m considered as a real vector space is equal to 2m, the necessary condition implies that p is an integer greater than or equal to 2m. This is why the requirement“p is an integer greater than or equal to 2 m” is an essential characteristic of this embodiment.

The multiple-input-port and multiple-output-port tuning unit (4) is such that it can provide, at said given frequency, for suitable values of the one or more tuning control signals, a low-loss transfer of power from the input ports to the output ports, and a low-loss transfer of power from the output ports to the input ports.

The specialist sees that the radio transceiver allows, at the given frequency, a transfer of power from the m input ports to an electromagnetic field radiated by the antennas. In other words, the radio transceiver is such that, if a power is received by the m input ports at the given frequency, a part of said power received by the m input ports is transferred to an electromagnetic field radiated by the antennas at the given frequency, so that a power of the electromagnetic field radiated by the antennas at the given frequency is equal to said part of said power received by the m input ports. The radio transceiver also allows, at said given frequency, a transfer of power from an electromagnetic field incident on the antennas to the m input ports. Additionally, the multiple-input-port and multiple-output-port tuning unit (4) and the antennas (11) (12) (13) (14) are such that, at said given frequency, for suitable values of the one or more tuning control signals, a low-loss transfer of power from the m input ports to an electromagnetic field radiated by the antennas can be obtained (for radio emission), and a low-loss transfer of power from an electromagnetic field incident on the antennas to the m input ports can be obtained (for radio reception). Thus, it is possible to say that the radio transceiver allows, at said given frequency, for suitable values of the one or more tuning control signals, a low-loss transfer of power from the m input ports to an electromagnetic field radiated by the antennas, and a low-loss transfer of power from an electromagnetic field incident on the antennas to the m input ports. The suitable values of the one or more tuning control signals are provided automatically. Thus, the specialist understands that any small variation in the impedance matrix seen by the output ports can be at least partially compensated with a new automatic adjustment of the adjustable impedance devices of the tuning unit.

The radio transceiver is a portable radio transceiver, so that the radio unit (8) also performs functions which have not been mentioned above, and which are well known to specialists. For instance, the wireless network may be a wireless communication network based on an LTE- Advanced architecture, or a wireless communication network based on a 5G New Radio architecture.

Figure 4 shows a possible resource grid (800) of the uplink of the wireless communication network. Here, the uplink of the wireless communication network uses single carrier frequency division multiple access (SC-FDMA) so that a data symbol (801) of the resource grid is an SC- FDMA symbol, corresponding to a known duration. Usually, SC-FDMA is regarded as orthogonal frequency division multiple access (OFDMA) with a DFT-based precoder. This is what is done in Fig. 4, where a subcarrier (802) of the resource grid corresponds to a known frequency interval, and where a resource element (803) corresponds to a data symbol (801) and a subcarrier (802). Thus, the data symbol (801) is also an OFDMA symbol.

The specialist understands that Z _Sant depends on the frequency and on the electromagnetic characteristics of the volume surrounding the antennas. In particular, the body of the user has an effect on Z _Sant , and Z _Sant depends on the position of the body of the user. This is referred to as“user interaction”, or“hand effect” or“finger effect”. The specialist understands that the radio transceiver may automatically compensate a variation in Z _Sant caused by a variation in a frequency of operation, and/or automatically compensate the user interaction.

In order to respond to variations in the electromagnetic characteristics of the volume surrounding the antennas and/or in the frequency of operation, a new adjustment sequence starts shortly after each change of the frequency of operation, and no later than 10 milliseconds after the beginning of the previous adjustment sequence.

In this first embodiment, N = n = m = 4. Thus, it is possible that N is greater than or equal to 3, it is possible that N is greater than or equal to 4, it is possible that n is greater than or equal to 3, it is possible that n is greater than or equal to 4, it is possible that m is greater than or equal to 3, and it is possible that m is greater than or equal to 4.

Second embodiment.

The second embodiment of a device of the invention, given byway of non- limiting example, also corresponds to the radio transceiver shown in Figure 3, and all explanations provided for the first embodiment are applicable to this second embodiment.

In this second embodiment, the radio transceiver uses the antennas simultaneously for MIMO radio communication. Additionally, in this second embodiment, the radio transceiver requests, from the wireless network, a permission to use, for excitations intended for an internal adjustment of the radio transceiver, one or more data symbols, and the radio transceiver specifies the one or more data symbols to which said authorization applies. More precisely,

the radio transceiver sends, to the wireless network, a radio signal requesting a permission to use one or more data symbols to send, inside one or more resource elements of said one or more data symbols, radio signals caused by excitations intended for an internal adjustment of the radio transceiver;

the radio transceiver specifies the one or more data symbols to which said permission will apply;

the wireless network sends a radio signal granting an authorization to use said one or more data symbols, each of said one or more data symbols being referred to as“authorized data symbol”; and

the radio transceiver is authorized to send, inside one or more resource elements of the one or more authorized data symbols, and only inside one or more resource elements of the one or more authorized data symbols, radio signals caused by excitations intended for an internal adjustment of the radio transceiver, said radio signals being not meant to be used by the wireless network to obtain information on the MIMO channel.

A full automatic adjustment of the multiple-input-port and multiple-output-port tuning unit requires several iterations, each iteration comprising the following steps: applying said m excitations to the m input ports; estimating said q real quantities depending on an impedance matrix presented by the input ports; delivering one of said tuning unit adjustment instructions; and delivering said one or more tuning control signals. Each of the excitations having a complex envelope, the complex envelopes of the m excitations are linearly independent in the set of complex functions of one real variable, regarded as a vector space over the field of complex numbers. Each iteration uses, for the excitations, only one authorized data symbol, and only m resource elements in this authorized data symbol, by utilizing the signal processing technique disclosed in the first embodiment of said international application number PCT/IB2015/057131 , and in the first embodiment of the patent of the United States of America No. 10,116,057.

Since said radio signals are not meant to be used by the wireless network to obtain information on the MIMO channel, each iteration does not use, for the excitations, one or more data symbols comprising resource elements allocated to reference signals for MIMO channel estimation. Thus, an iteration does not entail an incorrect estimate of the MIMO channel. Moreover, the authorized data symbols form a group that spans over a short period of time, so that a full automatic adjustment of the multiple-input-port and multiple-output-port tuning unit is sufficiently fast. Thus, we see that the invention overcomes the limitations of prior art. Third embodiment.

The third embodiment of a device of the invention, given by way of non-limiting example, also corresponds to the radio transceiver shown in Figure 3, and all explanations provided for the first embodiment are applicable to this third embodiment.

In this third embodiment, the wireless network specifies the one or more data symbols to which said authorization applies, that is to say, the authorized data symbols. More precisely, the wireless network sends a radio signal granting an authorization to use one or more data symbols, each of said one or more data symbols being referred to as“authorized data symbol”; and

the radio transceiver is authorized to send, inside one or more resource elements of the one or more authorized data symbols, and only inside one or more resource elements of the one or more authorized data symbols, radio signals caused by excitations intended for an internal adjustment of the radio transceiver, said radio signals being not meant to convey meaningful data, and said radio signals being not meant to be used by the wireless network to obtain information on the MIMO channel.

A full automatic adjustment of the multiple-input-port and multiple-output-port tuning unit requires several iterations, each iteration comprising the following steps: applying said m excitations to the m input ports; estimating said q real quantities depending on an impedance matrix presented by the input ports; delivering one of said tuning unit adjustment instructions; and delivering said one or more tuning control signals. Each of the excitations has a complex envelope, the complex envelopes of the m excitations being linearly independent in the set of complex functions of one real variable, regarded as a vector space over the field of complex numbers. Each iteration uses, for the excitations, only one authorized data symbol, and only m resource elements in this authorized data symbol, by utilizing the signal processing technique disclosed in the third embodiment of said international application number PCT/IB2015/057131, and in the third embodiment of the patent of the United States of America No. 10,116,057.

Since said radio signals are not meant to be used by the wireless network to obtain information on the MIMO channel, each iteration does not use, for the excitations, one or more data symbols comprising resource elements allocated to reference signals for MIMO channel estimation. Thus, an iteration does not entail an incorrect estimate of the MIMO channel. Moreover, the authorized data symbols form a group that spans over a short period of time, so that a full automatic adjustment of the multiple-input-port and multiple-output-port tuning unit is sufficiently fast. Thus, we see that the invention overcomes the limitations of prior art.

Fourth embodiment.

As a fourth embodiment of a device of the invention, given by way of non-limiting example, we have represented in Figure 3 the block diagram of a radio transceiver for communicating in a wireless network, the radio transceiver comprising: N = 4 antennas (11) (12) (13) (14), the antennas operating simultaneously in a given frequency band, the antennas forming a multiport antenna array (1);

a multiple-input-port and multiple-output-port tuning unit (4) having m = 4 input ports and n = N output ports, the multiple-input-port and multiple-output-port tuning unit comprising p adjustable impedance devices, where p is an integer greater than or equal to 2m = 8, the p adjustable impedance devices being referred to as the“adjustable impedance devices of the tuning unit” and being such that, at a given frequency, each of the adjustable impedance devices of the tuning unit has a reactance, the reactance of any one of the adjustable impedance devices of the tuning unit being adjustable by electrical means;

m sensing units (31) (32) (33) (34), each of the sensing units delivering two“sensing unit output signals”, each of the sensing unit output signals being determined by an electrical variable sensed (or measured) at one of the input ports;

N feeders (21) (22) (23) (24), each of the feeders having a first end which is directly coupled to a signal port of one and only one of the antennas, each of the feeders having a second end which is directly coupled to one and only one of the output ports; a radio unit (8), the radio unit receiving, from the wireless network, a radio signal providing an authorization to use, at a frequency referred to as the“selected frequency”, one or more data symbols, each of said data symbols being referred to as“authorized data symbol”, the radio unit being used to apply m excitations to the m input ports through the sensing units, one and only one of the excitations being applied to each of the input ports, each of the excitations having a carrier frequency which is equal to the selected frequency, the excitations existing inside one or more of the one or more authorized data symbols, the radio unit delivering“tuning unit adjustment instructions”, at least one of the tuning unit adjustment instructions being an“initial tuning unit adjustment instruction”, at least one of the tuning unit adjustment instructions being a“subsequent tuning unit adjustment instruction”; and

a control unit (6), the control unit receiving the tuning unit adjustment instructions, the control unit delivering one or more“tuning control signals” to the multiple-input-port and multiple-output-port tuning unit, the control unit generating, for each of the one or more tuning control signals, one or more values of said each of the one or more tuning control signals, each of said one or more values of said each of the one or more tuning control signals being determined as a function of at least one of the tuning unit adjustment instructions, the reactance of each of the adjustable impedance devices of the tuning unit being mainly determined by at least one of the one or more tuning control signals;

wherein:

for each of the one or more tuning control signals, said one or more values of said each of the one or more tuning control signals comprise an initial value determined as a function of one or more of the one or more initial tuning unit adjustment instructions; the radio unit estimates q tuning parameters, where q is an integer greater than or equal to m, by utilizing the sensing unit output signals, each of the tuning parameters being a real quantity depending on an impedance matrix presented by the input ports, said impedance matrix presented by the input ports being an impedance matrix presented by the input ports while each said initial value is generated; and

at least one of the one or more subsequent tuning unit adjustment instructions is determined as a function of:

one or more quantities determined by the selected frequency;

one or more variables determined by one or more of the one or more initial tuning unit adjustment instructions; and

the q tuning parameters.

An automatic adjustment of the multiple-input-port and multiple-output-port tuning unit uses, for the excitations, only one authorized data symbol, and only m resource elements in this authorized data symbol, by utilizing the signal processing technique disclosed in the sixth embodiment of the international application number PCT/IB2019/051501 of 25 February 2019, entitled “Method of automatic adjustment of a tuning unit, and apparatus for radio communication using this method”.

Since said radio signals are not meant to be used by the wireless network to obtain information on the MIMO channel, an automatic adjustment of the multiple-input-port and multiple-output-port tuning unit does not use, for the excitations, one or more data symbols comprising resource elements allocated to reference signals for MIMO channel estimation. Thus, an automatic adjustment of the multiple-input-port and multiple-output-port tuning unit does not entail an incorrect estimate of the MIMO channel. Moreover, only one data symbol is used, so that an automatic adjustment of the multiple-input-port and multiple-output-port tuning unit is very fast. Thus, we see that the invention overcomes the limitations of prior art.

INDICATIONS ON INDUSTRIAL APPLICATIONS

The method of the invention is a fast and accurate method for automatically adjusting a multiple-input-port and multiple-output-port tuning unit, and a fast and accurate method for automatically tuning an impedance matrix. The radio transceiver of the invention can quickly, accurately and automatically adjust its multiple-input-port and multiple-output-port tuning unit, to quickly, accurately and automatically tune an impedance matrix.

The method and the radio transceiver of the invention provide the best possible characteristics using very close antennas, hence presenting a strong interaction between them. The invention is therefore particularly suitable for mobile radio transmitters and transceivers, for instance those used in portable radiotelephones or portable computers.